Waterproof heating pad



Aug. 4, 1964 R. A. WISE 3,143,641

WATERPROOF HEATING PAD Filed Sept. 25. 1962 f)? ven 0)".- Pobert A. M'seUnited States Patent This invention relates to waterproof, flexibleelectric heating devices, such as heating pads, and more particularly tomeans for controlling the amount of air within such a sealed device.

An electric heating pad typically includes a flexible heating elementarranged in a suitable pattern and hermetically sealed within a flexiblecover material of plastic or rubber. A watertight heating pad isdesirable so that the device can be used with complete safety with wetpacks or where moisture is present without danger of electrical shock.However, manufacture of such a sealed heating device presents theproblem of control of the volume of air within the sealed enclosure. Iftoo much 'air is entrapped in the pad when the enclosure is sealed,

this air will expand when the heating element is energized, causing thepad to blow up like a balloon. Also, the air tends to insulate theheater from the user making the pad somewhat ineffective. On the otherhand, if the enclosure is evacuated before sealing, the pad will operatenormally, but will feel harsh and flat when applied to the body of theuser. Since a heating pad is usually applied directly against the skinof the user, smooth, comfortable flexibility is very desirable.

Accordingly, it is a primary object of this invention to provide awaterproof electric heating pad which feels soft and flexible at alltimes.

It is a further object of this invention to provide a waterproofelectric heating pad with an inexpensive arrangement to equalize theinterior pad air pressure with the exterior pressure throughout theentire temperature range to which the pad may be subjected.

In accordance with this invention, an electric heating pad is providedwith an air passage which permits air to flow freely into or out of thepad to maintain the pad in a soft and flexible condition. The pad itselfis provided with a waterproof, airtight cover which will permit it to betotally immersed in liquid or used with any type of wet pack. Thecontrol unit for the heating pad which is remote from the pad itself isnot hermetically sealed in that it is not expected to be immersed inwater. Pressure relief is obtained by forming an air passage within theelectrical power cord connecting the control unit to the pad. With thisunique and inexpensive arrangement, the pad will not feel hard and flatwhen cold and will not become inflated when hot, but yet the pad itselfmay be totally immersed without liquid entering the pad interior orcontacting any of the electrical wires. Furthermore, manufacture isfacilitated, since precise control of air content of the envelope at thetime of sealing is unnecessary.

Further features, objects and advantages will become apparent withreference to the following drawing in which:

FIG. 1 is a perspective view of an electric heating pad including a cordset and a control unit; and

FIGS. 2-5 are cross-sectional views of various cord set embodimentshaving an air passage therethrough.

Referring to FIG. 1 there is shown a typical electric heating pad 1having a resistance heating element 2 arranged on a suitable carrier 2aof felt or the like to distribute heat uniformly throughout the pad. Theheating element is enclosed within a cover or surface material 3 whichis flexible, waterproof, and washable. Rubberized fabric and sheetplastic films are commonly used for this purpose, such materials beingimpervious to air p CC and water. The cover 3 is hermetically sealedaround its outer periphery in any suitable manner; for example, by heatsealing a plastic or vulcanization of rubber.

Heating element 2 is connected by means of a conventional,multiconductor cord set 4 to a conventional control unit 5 having aplurality of pushbuttons 5a or other manually movable members to controlthe operation and temperature of the pad. Cord set 4 is, in turn,connected to power cord 6 terminating in a conventional electrical plug7 for connecting the heating pad to a conventional electrical outlet orother power source. Cord set 4 is preferably made of flexible,waterproof, electrically insulating material, such as plastic or rubber,and is hermetically sealed to the heating pad cover 3. The control unit5 is not designed to be immersed in water, and is accordingly not air orwatertight. Thus, the heating pad may be immersed in water or used withwet towels, and the cord set 4 may also be exposed to liquid up to itsconnection to the control unit 5.

If the heating pad cover 3 is completely sealed, a problem arises as tothe amount of air to be sealed within the cover at the time ofmanufacture. When the pad is in use, it should be flexible and pliable,so that it will conform to the contour of the users body. Also, the padsurface should not provide an unpleasant sensation to the user when incontact with the skin. Consequently, it is desirable to have a smallamount of air entrapped within the cover to obtain a soft, pleasanteffect. However, the amount of air employed must be limited, in that anexcess amount of air would materially reduce the efficiency of theheater by acting as an insulator between the user and the heatingelement 2. In other words, if too much air is sealed within the cover 3,such air will expand responsive to heat, and the cover will tend toinflate like a balloon.

On the other hand, if only sufficient air is sealed within the pad toprovide the proper effect when the pad is in use, the pad tends to feelharsh and flat to the touch at lower temperatures. If a partial vacuumexists within the sealed envelope 3, the fabric or felt carrier iscompressed, and the pattern of heating wire 2 is clearly apparent on theoutside of the pad. Under these circumstances, the pad is not conduciveto the comfort which the user seeks by heat therapy.

In accordance with the present invention, the air pressure problem issolved by a unique and simple arrangement wherein an air pressure reliefmeans is formed within the cord set for the heating pad withoutsacrifice of the waterproof qualities. This is accomplished by providingan air passage in the cord set between the interior of the pad and theinterior of the control unit. Since the control unit is not sealed, theinterior of the heating pad is in effect kept at atmospheric pressure.Such an arrangement gives the desired feel to the heating pad throughoutthe entire temperature range to which the pad is normally to besubjected.

The air passage within the cord set may be provided in a variety ofways. In FIG. 2, there is shown the cross-section of a conventional riptype cord set 8 composed of juxtaposed sections 9, 10, 11, and 12, allbut one provided with a conducting wire 13, 14, and 15, respectively.Section 11 is formed with an air passage 16 extending from the pad tothe control unit, so that air may flow to and from the heating pad. Acord set 8 having such an air passage may be easily and inexpensivelyfabricated by using known extrusion techniques. FIG. 3 shows a cord setwhich is identical to FIG. 2 except that a noncollapsible tube 18 ispositioned within section 11 of the cord set. The tube 18, beingnoncollapsible, will prevent the air passage 19 from being inadvertentlypinched or squeezed closed. Such an arrangement is slightly moreexpensive than the arrangement shown in FIG. 2, but has the advantage ofbeing more reliable, trouble free, and easier to heat seal to thewaterproof cover.

FIG. 4 shows a three sectioned or stranded cord set 20, in which one ofthe conductor groups 21 is given a tubular shape rather than theconventional solid crosssection. To prevent the air passage 22 formedwithin the conductor 21 from being inadvertently closed, there isprovided a noncollapsible tube 23 positioned within conductor 21. Theends of the conductor 21 and tube 23 must, of course, be left openwithin the pad and within the control unit to permit air flow. Theembodiment of FIG. 4, requiring only a three-stranded cord set, has theadvantage of being more compact than those of FIGS. 2 and 3.

I11 FIG. 5, there is shown an embodiment of a cord set wherein thegrooves formed between the strands of a conventional cord set 24 of thetype shown in FIGS. 23 have been enclosed to form a plurality of airpassages 25-28. Cord set 24 presents a fiat rectangular cross-sectionwhich has the advantage of being easily scalable to the heating padcover. Although the number of passages formed within cord set 24 isentirely optional, forming a plurality of passages provides reliabilityto the heating pad in the event one or more of the passages shouldbecome clogged in any manner.

It will be appreciated that an air passage may be inexpensively formedwithin the cord set in a variety of other arrangements which willreadily come to mind. Accordingly, it should be understood that theinvention is not limited to the particular cord set cross-sectionsshown, and it is intended in the appended claims to cover all suchvariations and modifications that fall within the true spirit and scopeof this invention.

What I claim is:

1. An electric heating pad having a flexible cover which is imperviousto air and water, a resistance heating element distributed within saidcover, an unsealed heating pad control unit, a flexible, electrical cordset including a plurality of conductors and having a cover materialwhich is impervious to air or water, said conductors being connected tosaid heating element said cord set having one end sealed to said heatingpad and its opposite end connected to said control unit, a power cordconnected to said cord set at one end and adapted for connection to apower source at the other end, and pad air pressure relief means formedwithin said cord set which equalizes the-air pressure within and withoutthe pad even though water cannot enter the pad when it is totallyimmersed in water.

2.'An electric heating pad having a flexible, waterproof, airtightsurface material, a resistance heating element distributed within saidcover, an unsealed heating pad control unit, a flexible waterproof powercord sealed to said pad, at one end and connected to said control unitat its other end, said cord including an air passage '4 formed thereinto provide air pressure relief means for the pad.

3. An electric heating pad having a flexible airtight cover material, aresistance heating element distributed within said cover, an unsealedcontrol unit for the pad, a flexible airtight cord set having one endhermetically sealed to said pad and the other end connected to thecontrol unit, means for connecting said cord set to a power source andpad air pressure release means formed within said cord set comprising anair passage extending between the pad and the control unit.

4. An electric heating pad having a surface material which is imperviousto air and water, a resistance heating element distributed within thepad an unsealed heat control unit for the heating pad, a flexibleairtight cord set connecting said pad to the control unit, said cord setincluding a plurality of conductors embedded in a cover of insulatingmaterial, said conductors being connected to said heating element, and anoncollapsible tube embedded within said cord set and extending betweenthe pad and the control to provide air pressure relief means for thepad.

5. A flexible electric heating pad having a waterproof cover, aresistance heating element distributed within said cover, a heat controlunit for said pad which permits air flow into and out of the controlunit, a cord sealed to said pad and connected to the control unit, astranded, tubular-shaped conducting wire included within said cord whichprovides an air passage between said pad and said control unit.

6. An electric heating pad having a flexible airtight surface material,a resistance heating element distributed within the pad, a control unitfor the pad which permits air flow into and out of the control unit, aflexible air.- tight electrical cord set connecting said pad to thecontrol unit, said cord set including a plurality of conductors embeddedin insulated juxtaposed relation, in an airtight cover material, saidconductors being connected to said heating element, a'power cordconnected to said cord set at one end and adapted for connection to thepower source at the other end, and a plurality of air passages formedwithin said cover material adjacent said conductors extending betweenthe pad and the control unit to provide air pressure relief means forthe pad.

References Cited in the file of this patent UNITED STATES PATENTS490,891 Ahearn Jan. 31, 1893 1,994,759 Dermott Mar. 19, 1935 1,997,899Dick Apr. 16, 1935. 2,617,011 MacKendrick Nov. 4, 1952 2,735,926Langlois Feb. 21, 1956 2,758,194 Heron Aug. 7, 1956 2,776,385 ModreyJan. 1, 1957 2,873,352 Franco Feb. 10, 1959 2,910,524 Schaflhouser Oct.27, 1959

2. AN ELECTRIC HEATING PAD HAVING A FLEXIBLE WATERPROOF, AIRTIGHTSURFACE MATERIAL, A REISISTANCE HEATING ELEMENT DISTRIBUTED WITHIN SAIDCOVER, AN UNSEALED HEATING PAD CONTROL UNIT, A FLEXIBLE WATERPROOF POWERCORD SEALED TO SAID PAD, AT ONE END AND CONNECTED TO SAID CONTROL UNITAT ITS OTHER END, SAID CORD INCLUDING AN AIR PASSAGE FORMED THEREIN TOPROVIDE AIR PRESSURE RELIEF MEANS FOR THE PAD.